Ultra Low NOx Gas Turbine Combustion Monday 16 - Friday 20 January 2017

Transcription

1 Ultra Low NOx Gas Turbine Combustion Monday 16 - Friday 20 January 2017 Programme Monday 16 January 2017 Fundamentals of NOx Formation 08:00 Registration and coffee 08:30 Introduction & GT cycles for low carbon and carbon sequestration, implications for NOx Environmental concerns of NOx. Future trends in gas turbine combustor operating conditions. Relationship between legislated parameters, emission index, NOx corrected to 15% oxygen and NOx g/km and g/kwhr. H2 as a GT fuel, no carbon emissions if source is green, but potentially increased NOx. HC fuel/o2 cycles. IGCC with carbon sequestration to yield green hydrogen. EGR cycles to increase exhaust CO2 levels for CCG. 10:45 Coffee 11:00 Thermal NOx formation kinetics (part 1) NOx kinetics, influence of inlet temperature, dependence on adiabatic flame temperature for well mixed mixtures and relative low dependence on the inlet temperature for the same flame temperature. Experimental evidence in well mixed systems for constant NOx at different inlet temperatures but the same flame temperature. Consequence of any near stoichiometric operating regions. Thermal NOx prediction techniques for CFD. NO2 formation in low NOx GT 13:30 Thermal NOx formation kinetics (part 2) 15:00 Thermal NOx control techniques Water or steam injection, lean well-mixed combustion, rich/lean combustion. 15:30 Tea 15:45 The pressure dependence of NOx - experimental evidence reviewed The evidence for a 0.5 pressure exponent for thermal NOx. Correlations used by different manufacturers for the pressure effect on NOx. Evidence of the uncertainty in the NOx pressure exponent for lean well mixed gas turbine combustors and evidence that there is no pressure dependence for very lean well mixed systems. 16:15 Flue gas recirculation in low NOx gas turbines for enhanced exhaust gas CO 2 to enable viable CCS to be applied Conventional gas turbine combustors have a significant NO2 emission at low powers. Some low NOx gas turbines have relatively high NO2 as a proportion of the low NOx. Reheat systems or reburn systems where extra fuel is burnt in the exhaust products of upstream combustion also generate high NO2. The kinetic reasons behind this occurrence are outlined. 17:00 Prompt NOx, including N 2O kinetics Prompt NOx or non-thermal NOx is present in lean low NOx systems as the source of the remaining NOx. For gas turbines with single digit NOx the source of NOx is prompt and includes the N2O mechanism. 17:20 Nitrogen dioxide emissions and formation Conventional gas turbine combustors have a significant NO2 emission at low powers. Some low NOx gas turbines have relatively high NO2 as a proportion of the low NOx. Reheat systems or reburn systems where extra fuel is burnt in the exhaust products of upstream combustion also generate high NO2. The kinetic reasons behind this occurrence are outlined. 17:40 Fuel nitrogen NOx - the importance of low level fuel nitrogen in NOx emissions from liquid fuels such as gas oil Importance of low level fuel nitrogen in gasoline and diesel in meeting ULEV legislation. Requirement for rich/lean combustion if fuel nitrogen level is high. 18:00 End of day one 18:15 Welcome reception in the Stables Bar, Weetwood Hall

2 Tuesday 17 January 2017 CO Emissions, Film Cooling, Flammability, Flame Propagation, Weak Extinction and Flashback 08:30 CO and hydrocarbon formation and destruction Equilibrium CO variations with equivalence ratio, inlet temperature and flame temperature. Comparison of CO emissions with lean well mixed combustion and equilibrium CO. CO oxidation global kinetics and the influence of residence time. Evidence for lean well mixed systems following equilibrium CO until for lean mixtures there is insufficient residence time and CO suddenly increases. Influence of mixing imperfections in increasing CO emissions. Critical temperature range of low NOx with low CO and UHC. 09:45 The influence of film cooling on CO, UHC and NOx emissions and the requirement of no primary zone film cooling for minimum NOx and CO emissions Evidence will be reviewed from a number of manufacturers to show that the lowest NOx emissions are achieved with no wall film cooling in the lean well mixed region. Any film cooling air forces the lean combustion to be proportionately richer with higher NOx emissions. Evidence will also be reviewed for reduced CO and UHC emissions as film cooling air is reduced. A systematic study of the addition of film cooling to a dump expansion radial swirler with passage fuel injection will be used to show that the greatest influence on the film cooling is on the NOx emissions. The increase in CO emissions is directly related to equilibrium CO effects rather than CO quenching. 10:45 Fundamentals of laminar and turbulent pre-mixed combustion and flammability limits Measurement of premixed gas/air flammability limits, influence of inlet temperature up to 1300K, gaseous and liquid fuels, influence of pressure. Concept of critical flame temperature at the lean limit. Prediction of lean limits for hydrocarbon fuels and for low CV gaseous fuels. The influence of pressure on the lean limit Demonstration that the lean limit for well atomised sprays is the same as for gas/air mixtures. 11:45 Weak extinction and lean flammability limits in premixed / prevaporised combustion Influence of flame stabiliser design on weak extinction. Demonstration that the flame stabiliser design influences the weak extinction for premixed systems, large recirculation zones good for flame stability. Influence of inlet temperature and pressure on weak extinction and comparison with the flammability limits. Review of premixed weak extinction data for baffle and swirl flame stabilisers, including Leeds data for a wide range of baffle stabiliser and axial and radial swirler designs with co and counter swirl. Concept of weak extinction blow-off velocity being the area averaged turbulent burning velocity. 13:30 Flame stability requirements of gas turbine combustors and their incompatibility with single stage low NOx combustors. Fuel staging or air staging? 14:00 Turbulent flame propagation in premixed fuel/air mixtures Dr Roth Phylaktou, Energy Research Institute, University of Leeds Turbulent burning velocities in premixed mixtures control premixed flame weak extinction and the risk of flashback in premixing ducts. Key turbulence parameters that are used in turbulent burning velocity correlations and regime diagrams are reviewed. The experimental data for highly turbulent flames and the correlations and theoretical predictions of turbulent flame structure regime for premixed gas turbines is reviewed. Influence of turbulent length scale on turbulent burning velocity, 15:15 Tea 15:30 Premix/prevaporisation duct design and NOx emissions Results are reviewed for full premixing i.e. 1-2m upstream pipe as a mixing length. Work done by NASA, Leeds and others more recently. NOx results for baffle and swirl stabilisers. Axial and radial, single and double, swirlers with co and counter swirl. Demonstration that large recirculation zones are bad for NOx and that premixed flame NOx emissions are sensitive to the stabiliser design. I Vaporisation time and length for different inlet temperatures and pressure II Spontaneous Ignition time at different inlet temperatures and pressure III Flash back - minimum flow velocity requirements IV Compromised design criteria for a premixing duct, for temperatures up to 1200K. Comparison of premix ducts used in some low NOx gas turbine combustors. V Reasons for using rapid fuel and air mixing at the stabiliser plane or within the stabiliser.

3 Tuesday 17 January 2017 (Continued) 17:00 Air staging low NOx combustors Air staging offers the possibility of operating the lean combustor at constant lean equivalence ratio and low NOx as the power is varied. Different techniques for achieving air movement between the lean primary zone and the downstream dilution zone are reviewed. 18:00 End of day two Wednesday 18 January 2017 Premixed Low NOx Combustors and the Importance of Fuel/Air Mixing 08:30 Lean low NOx acoustic instabilities and pressure oscillations I Review of experience with acoustic problems in LPP low NOx combustors. Importance of the premix duct time constant and the distance between the fuel injection holes and the combustor inlet, use of pilot fuel to control the acoustic oscillations, use of side resonator tubes as passive acoustic control measures. Influence of LPP equivalence ratio, role of acoustics in creating air and fuel flow fluctuations which reinforce the oscillations. Methods developed to control the problem by various manufacturers. 10:15 Coffee 10:30 Lean low NOx acoustic instabilities and pressure oscillations II 12:00 Low NO x Technology: Premixed and Staged Combustors Felix Güthe, GE Power This presentation will show the development of lean premix combustion technologies. Burners with short but effective premixing zones (EV burners: environmentally friendly V-shaped burners and AEV burners) have been implemented in gas turbines with low and ultra low NOx levels. Staged fuel injection is the latest development step for premix burners achieving even lower NOx levels and increased flexibility. In the context of ultra low NOx technologies reheat combustion and flue gas recirculation are briefly mentioned. The low emission capabilities and the generic operational and fuel flexibility of staged combustion systems are discussed starting from fundamental kinetics and design concepts. 13:00 Lunch 13:45 The importance of flame stabiliser pressure loss on fuel/air mixing and NOx: experimental evidence The energy for turbulent mixing of fuel and air comes from the stabiliser pressure loss. This creates the kinetic energy of turbulence. The magnitude and location of which can be predicted using CFD and aid the selection of the fuel injection location so that the fuel and air mixing utilises the peak turbulent kinetic energy. Isothermal measurements of fuel distribution and turbulent fuel/air mixing. Experimental traverses of lean low NOx flames to illustrate the uniformity of mixing required. Demonstration by several manufacturers and Leeds work that direct fuel injection into swirling and non-swirling jet shear layers can produce mixing that is better than 10% of the mean with fluctuations in mixing that are less than 10% of the mean. Most manufacturers are now achieving 5% fluctuations from the mean. 14:45 Tea 15:00 Air assist atomisation of liquid fuels Requirements for simultaneous atomisation, mixing and flame stabilisation. Experimental results for large air flow lean primary zone air blast flame stabilisers for lean low NOx applications. 15:45 Liquid fuels (including alternative fuels) for gas turbines and their impact on combustion, emissions and deposits formation Dr Hu Li, Energy Research Institute, University of Leeds 16:30 Non-swirling baffle type combustors Non-swirling baffle type combustors with direct fuel injection with each air injection point. Simple conversion of a grid plate premixed flame stabiliser into a lean gas turbine combustor, UTRC and Leeds work on the Grid Mix combustor. The AIT and Leeds Jet Mix system with gaseous and liquid fuels. Internal gas composition traverses of the lean combustion. The use of conical grid plates with central fuel injection for a large turn down ratio and reasonably low NOx on gas and liquid fuels. 17:00 End of day three

4 Thursday 19 January 2017 Practical Lean Ultra Low NOx Combustors I 08:30 Axial swirl lean combustion Large air flow capacity dump expansion axial swirlers with central, swirler outerperiphery and upstream/downstream fuel injection. Illustration from Leeds work of 1-2 ppm NOx by natural gas and 5ppm with kerosene. Internal gas composition of the lean combustion flames. Examples of practical use of axial swirlers with Allison, KHI, GE and Solar. Siemens/KWU swirl burner Radial swirl lean combustion Large air flow capacity dump expansion radial swirlers with central or passage or swirler outlet wall fuel injection, as developed at Leeds and exploited by Alstom Power UK. Internal gas composition traverses of the flames with passage fuel injection and 1-2ppm NOx. Demonstration that the design of the radial passages is not too critical: curved blade, straight passage, round hole and aerodynamic blades all have similar results for the same fuel location. Application of CFD to the prediction of radial swirl combustion. Comparison with Alstom Power UK results on the Tornado, Tempest and Typhoon engines. 10:45 Counter-rotation axial swirlers Counter-rotating dump expansion large air flow swirlers. Leeds work with fuel injection into the counter-rotating shear layer and associated CFD work. Survey of applications by GE, KHI, Tokyo Gas and others. 11:45 Counter-rotating radial swirlers Counter-rotating radial swirlers with dump expansion, dual and upstream passage fuel injection, central injection, combined central and passage fuel injection. Applications in the Rolls-Royce RB211 and Trent industrial gas turbines and with Volvo. Addition of premix staged combustion with Rolls-Royce. 13:30 The development process applied to Siemens Industrial Turbomachinery s dry low emission combustion technology Dr Ghenadie Bulat, Siemens Industrial Turbomachinery Dry low emission technology has reached the stage where guarantees of <25ppm NOx on gas operation is commonplace. Siemens Industrial Turbomachinery's range of small gas turbines operate with a dual fuel dry low emission system which also guarantees <50ppm NOx on liquid operation. There is an increasing trend towards yet further reductions in emissions, whilst improving aspects related to robustness, cost and operability. This has required a change in the traditional highly-empirical development process, since far greater understanding about the underlying mechanical / physical / chemical processes is now required. The development process is evolving such that empirical approaches are increasingly supplemented by detailed numerical and theoretical models. The presently adopted process, which utilises a range of empirical and detailed numerical methods, will be described by way of an example where dry low emission technology is being extended towards ultra low emissions levels. 14:30 Development of the hybrid burner for the Siemens Gas Turbines Dr Holger Streb, Siemens AG Power Generation, Mülheim, Germany The development from Siemens gas turbines with silo combustor to the anular combustor was a milestone in gas turbine history which lead the new generation to higher turbine inlet temperatures, more power output and lower emissions. The different steps in development of the combustion and burner system are described for the natural gas and fuel oil operation. Results from the Berlin test bed and customer operated engines showed the reliability of the combustion system with low emissions. 15:30 Tea 15:45 Fuel staging low NOx combustors The staging of fuel between two or more air and fuel stages. Fuel staging in a single plane e.g.khi and GE Low NOx I and II Rolls-Royce axial fuel staging. Pilot and main staging in the same axial plane. GE Aero three stage axial swirlers. Aero gas turbine prototype fuel staging low NOx designs. 17:15 End of day four 19:00 Course dinner

5 Friday 20 January 2017 Practical Ultra Low NOx Combustors II 08:30 Combustor Development for Aeroderivative Industrial Gas turbines Gilles Bourque, Siemens Canada Ltd 09:30 Low NOx Combustor Development for Aero-Engines Marco Zedda, Rolls Royce plc Design approaches being investigated. The problem of turn down and relight. Fuel staging or air staging? 10:45 Gas Turbine Combustion Evolution Marcus Scholz, GE Energy, Europe Sustainable gas turbine technology development within confines of current legislation. Evolution of GT technology and market requirements in the context of emission control and economic parameters. Validation and testing results of advanced, high efficiency Gas Turbines, applying advanced fuel staging at elevated firing temperatures, whilst maintaining low NOx capability. 11:45 Gas Turbines for Syngas & Hydrogen Combustion Marcus Scholz, GE Energy, Europe The future of Carbon constrained power generation requires gas turbines to be fuel flexible and capable of handling high hydrogen fuels. Integrated Gasification Combined Cycles (IGCC) are based on reliable gasification technology and can use commercial proven Carbon Capture technology with subsequent hydrogen fuel being utilized in large industrial gas turbines. Extensive experience exists with utilizing high hydrogen fuels in gas turbines and further development is undertaken to also apply this type of fuel in premix combustion systems. 12:15 Lunch 13:00 Low NO x Technology Andrea Ciani, Ansaldo Energia This presentation will show the development of lean premix combustion technologies of gas turbines. Burners with short but effective premixing zones (EV burners: environmentally friendly V-shaped burners) have been implemented in all new gas turbines with NOx levels well below 25 ppm. Staged fuel injection is the latest development step achieving even lower NOx levels and increased flexibility. A further step in the reduction of emissions is obtained by introducing the reheat architecture in the GT26/GT24 using SEV burners in a second combustion chamber. Reheat combustion has proven now in over 100 units to be a robust, and highly flexible gas turbine concept for power generation. Two key topics explain the intrinsic advantage of reheat combustion to achieve ultra-low emission levels. First, the fundamental kinetic and thermodynamic emission advantage of reheat combustion is discussed analyzing in detail the emission levels of the first and second combustor stages, optimal firing temperatures for minimal emission levels, as well as benchmarking against single-stage combustion concepts. Secondly, the generic operational and fuel flexibility of the reheat system is emphasized, which is based on the presence of two fundamentally different flame stabilization mechanisms, namely flame propagation in the first combustor stage and auto-ignition in the second combustor stage. 14:30 Lean/lean fuel staging without air staging and Rich/lean low NOx combustors One technique to overcome the flame stability and turn down problems lean low NOx combustion systems is to operate a two stage system with all the fuel in the first stage with an initial rich zone followed by a downstream air injection zone with quick quenching. These designs are essentially where there is a high fuel nitrogen content are ammonia content in coal gasified gases, but they offer a solution to the turn down problem without air or fuel staging and are applicable to aero-gas turbines. Recent publications in these areas are reviewed. 15:45 Tea 16:00 Catalytic combustion for low NOx gas turbines A review of recent developments comparison with the best lean premixed combustors. Catalytic combustion works best where the compressor exit temperature is above the catalyst light off temperature. However, this is not often the case and a pilot is used which often compromises the NOx emissions. Partial heat release catalyst with downstream heat release and fuel injection are also reviewed. 17:00 End of day five and course